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03/14/2000
P. piscicida - Jekyll and Hyde and More
Today''s Marco Daily News reports that the red tide along the
southwest coast of Florida appears to be diminishing in intensity.
Actually, if the conches and vultures (see earlier column) were
due to the red tide, I personally found it quite intriguing. So, I
felt relatively unconcerned until I picked up last August''s issue
of Scientific American and read JoAnn Burkholder''s article "The
Lurking Perils of Pfiesteria." Now, I''m truly frightened! Ms.
Burkholder is professor of botany at North Carolina State
University and the world''s foremost authority on Pfiesteria,
particularly Pfiesteria piscicida. Pfiesteria is a member of a
group of characters known collectively as "harmful algae."
Certain of these harmful algae are responsible for the
aforementioned red tide and for the "algae blooms" which result
in large-scale fish kills. The kills can be the result of toxins
released into the water by some harmful algae or of the algae
blooms simply using up the oxygen needed to sustain the marine
life.
The term "harmful algae" is actually not strictly accurate. Some
of its members are true algae, primitive plants which make
chlorophyll and their own food through photosynthesis.
Pfiesteria, on the other hand, are not plants but single cell
organisms known as dinoflagellates. These dinoflagellates are
creatures that at some stage in their existence have these tails
(flagella) that whip around driving the organism through the
water. Pfiesteria piscicida, let''s call it pfisty from now on, looks
like a sperm except that Pfisty''s head looks more like a round
ball with a ring around it, sort of like the planet Saturn. Another
form has not one but two tails. In fact Pfisty is truly an amazing
and frightening creature, a Dr. Jekyll and Mr. Hyde of the marine
environment. For example, depending on conditions, it can
change into 24 distinct forms. It can change its size, becoming
over a hundred times larger in under 10 minutes. It can change
from a benign bacteria-eating diner to a toxin-spewing
hunter/killer/devourer of fish.
Pfisty''s different forms are so varied that you would never
recognize them as being the same single-celled creature. They
range from the planetary things with tails to round balls with
spikes like a sea urchin to amoebas of various sizes, some
resembling starfish. Pfisty can also turn into round cysts that are
pretty tough objects. Pfisty likes to turn into a cyst and hibernate
when the water gets rough and swimming gets difficult.
Burkholder described some experiments in which 20% of the
cysts survived various tortures such as drying for 35 days,
dousing them in concentrated acid or alkali or even putting them
in bleach for an hour.
To witness Pfisty in action, let''s take a typical scenario. Pfisty
usually hangs around in three basic forms: #1, hibernating cysts;
#2, amoebas browsing on algae or other delights in the mud
bottom; #3, nontoxic swimmers called zoospores (our sperm-like
critters). All is rather peaceful until the fish enter the area.
Pfisty #3 quickly transforms into a toxic zoospore, starts spewing
out toxins and swims towards the fish. The commotion alerts
Pfistys #1 and #2, who gradually transform first into nontoxic
zoospores and then into toxic zoospores and the attack on the fish
intensifies. The toxins destroy the skin of the fish, allowing
various bacteria and fungi to join the fray. To make matters
worse for the fish the toxic zoospores reproduce to form smaller
versions of themselves called pametes, which promptly group
together to form large swimmers called plano-zygates. These
guys love to suck in bits of skin and other stuff leaking from the
sores on the fish - a ghastly picture! Finally, when the fish die,
many Pfistys turn into amoebae that lock onto the fish for a
leisurely repast.
In 1991, the year Pfisty was first linked to a major fish kill, a
billion fish died in the estuary where the Neuse River in North
Carolina mixes with the salt water of the Atlantic Ocean. It turns
out that North Carolina is not a great place for a Pfisty presence.
Apparently, about half the fish along the whole East Coast of the
U.S. are at some stage of their life cycle involved with North
Carolina''s estuaries. Pfisty''s effects not only include fish kills
but at various levels may lead to non-hatching of eggs and
sublethal damage to fish which result in depletion of the whole
fish population. Pfisty has now been found in coastal areas from
Chesapeake Bay down around Florida to the Gulf coast of
Alabama.
We''ve seen that Pfisty really has it in for the fish but what about
us? Consider the personal experiences of Prof. Burkholder''s
colleague Howard Glasgow, a cheerful, very sharp scientist who
made the mistake of trying to clean up the walk of a lab
contaminated with Pfisty''s toxin. It wasn''t realized for some that
the toxin can take the form of an aerosol which can be inhaled.
Well, after starting to wipe down the walls, Glasgow began to
gasp for breath, lost his coordination, vomited and just managed
to crawl out of the lab. That lab was abandoned in favor of a
new, "carefully ventilated" facility. Ironically, the contractor,
believe it or not, vented the air from the toxic culture lab directly
into Glasgow''s office! Over the next several months, he became
a moody, disoriented fellow - who suffered both long - and
short-term memory losses. Glasgow finally had to take a couple
months off work when he could no longer remember his phone
number or find his way home. He recovered but, even a couple
years later, suffered various aches and pains as well as periods of
disorientation. Burkholder herself has suffered from chronic
bronchial infections and many bouts of pneumonia.
In 1997, there were small outbreaks of Pfisty in the Chesapeake
Bay region. Fishermen who spent their lives fishing the Bay
found themselves getting lost and disoriented in familiar areas.
Of course, the question arises as to the hazards of eating fish
exposed to sublethal doses of "harmful algae" toxins.
Burkholder bemoans the fact that scientists don''t have a
thorough knowledge of either the life cycles of the "algae" or the
chemical compositions of the toxins. Furthermore, outbreaks of
harmful algae seem to be increasing in frequency and over wider
areas of the globe. Of course, global warming is postulated as a
possible factor in the increasing range of algae bloom. The
blooms are also related to increasing pollution of our waterways
by nutrient-rich runoffs from waste disposal, farming and
livestock operations, etc.
Having just enjoyed, the second grouper sandwich of our stay
here, I wasn''t too thrilled by Burkholder''s statement that some
dinoflagellates produce so-called ciguatera toxins that
accumulate in reef fish without killing them. According to
Burkholder, ciguatera-containing barracuda, red snapper, grouper
and other tropical fish cause more human illness than any other
seafood poisoning. Other dinoflagellates produce saxitoxins,
which sometimes lead to fatalities from consumption of
contaminated shellfish.
Fortunately, I never have taken to raw clams or oysters - guess
I''ll take my chances with the grouper sandwich!
Allen F. Bortrum
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